Creating Electricity Using the Motion of the Body

Piezoelectric energy harvesters can be used to power more wearable electronics in the future.

Michael D’Agati ‘18

Wearable electronics, such as the Fitbit and Apple Watch, have started to flood the consumer marketplace. Flexible energy sources, rather than traditional batteries, are garnering more popularity to power this wearable technology because energy created by a moving human body – an unlimited power source – can be harvested and used to power them. A team of researchers led by Dr. Xingzhao Wang from Shanghai Jiao Tong University in Shanghai, China recently developed a flexible, transparent energy source – a biocompatible single-friction-surface transparent triboelectric and piezoelectric hybrid generator that can be worn on the neck, finger, elbow, or ankle to power long-time wearable self-powered devices.

This device can be used through one of two methods: the triboelectric method or piezoelectric method. The first method generates electricity due to frictional forces, while the latter generates electricity due to mechanical stress from outside pressures on the material. The hybrid device developed in this project used aluminum doped zinc oxide as transparent electrodes and poly(vinylidenefluoride-co-trifluoroethylene), a ferroelectric polymer, as a piezoelectric functional layer. Polydimethylsiloxane was used to create a micro pyramid structure for the triboelectric layer. To test the hybrid device, the team attached the generator to the surface of the forearm. The maximum output voltage from triboelectric means was 25 V and the maximum output voltage from piezoelectric means was 2 V, which is relatively low, compared with typical piezoelectric generators. The authors noted that the device would be improved by including optimized pyramid structures and electrospinning the nanowire film. The results showed that as the load resistance increased, the output voltages for both methods also increased.

The device developed in this project successfully showed that mechanical energy could be harvested from the human body by triboelectric and piezoelectric means. These two methods were integrated into a single hybrid device, which was tested on a human forearm and produced a total obtained output voltage of 26 V. This project shows the ability to integrate multiple energy harvesting techniques into one device. In the future, one device could possibly hold many techniques, or, have an energy harvesting device as well as a way to store that energy for future use.